Process for the production of fuel gas from carbonaceous solid fuels



Patented May 6, 1952 UNITED STATES PATENT OF F ICE Du Bois Eastman,Whittier, Calif., assignor to The. Texas Company, New York, N. Y., aconporation of Delaware Application June 15, 1949, sei-iai No. 99,182v

claims. (CI. 1s- 202) This invention relates to a process forthe-production of fuel gas from a carbonaceous solid fuel. In one ofits-more specific aspects this invention relates to an improvedl processfor the distillation of coal and the simultaneousmethanizati'on ofcarbonY monoxide and hydrogen to produce a fuel gas of relatively highheating value. The process of this invention may beV applied to thegasification ofv coke, oil shale, and various grades off' coal includinganthracite, lignite; and bituminousv coals.

Anobject of this invention is to provide an improved process for the`gasification of solid carbonaceousfuels.

Another object of this invention is to provide for the productionoffuelgas from` solid fuels.

Still another object of this invention is to provide for thedistillation of volatilizable constituents from solid carbonaceousmaterials containing volatilizable constituents'.

Alfurther objectof` this invention is to provide for themethanization ofcarbon monoxide and hydrogento -produce a fuel gas of high heatingvalue;

In aicopending application of du'Bois Eastman and Leon-V P. Gaucher,Serial No. 49,626, led September 16, 1948, (D#31,-208), a novel processfor pulverizing carbonaceousv solidsis disclosed. InaccordanceWiththe-method disclosed in said application, particles of a solid-carbonaceous material, particularly coal, are admixed with a liquid to.form-a` suspension and the suspension `passed asa coniined streamthrough a-heating zone. The carbonaceo-us solid is heated in the heatingzone to` an elevated temperature. Heatingoffparticles of..coal.underthese conditions resultsA inrapid disintegrationof the particles topowder.

In accordance .with the presentinvention, this novel step" of heating.and pulverizing solid Acarbonaceous.. material is employed inconnection withI gasification .of the `resulting powdered `fuel withQXygen and steam and conversion of the resulting, carbon monoxide andhydrogen to fuel gas.: The gasification with steam'and oxygen is carriedout ina lliow type-gas .generatcr'at a temperature Within the-.rangeofvfrom about `2000 vto about 3000 F. Hotagasesfrom the gasication stepare used tosupplyfheat for carbonization of the fuel in al fluidized bedin' a separate carbonizration and methanizationi zone.l Themethanization zone is'operated' at Va temperature withinthe rangezoffrom about 900 to'about 1800 F; and preferably` within* the range'ofyfrom about 1000 to about :1500F. Additional heat is liberated -bythemethanization reaction, ige., the reactionof carbon monoxide-andhydrogen toproduce methane. that liberated from the fuel by distillationserve to enrich the product gases. Heat from thega'si'- cation is alsoused for heating the' slurry to vaporize thefliquid and-preheatandva'porizef the carbonaceo'us solid.

An important distinction'over processes" of the priorv art is thecombination of anI unobstructed, now type generator'and a fluid bedcarbonization zone. The results obtainedby this combination arequantitatively different from thosevobt'ained by fluid bed gasificationprocesses and'thosefelnploying moving beds. In the iioW type' generator,thefquantity of solid luel supplied to the generatoi" is justsuliicient' to react with the gases. Slag maybe Withdrawn fromthegenerator asfaliquid or solid'ash maybe separated from' the productgases. Free heat transfer by'radiation is achieved so that the entirereaction zone operates at es'- sentially a single uniform temperature;For best results the internal surface area of the generator, as comparedwith the surface ofv av sphere of equal volume, is less than 1.5 timesthe surface area of the sphere. A

Methanization is most 'effectively carried out ata temperatureconsiderably below the temperature eliective for' rapid and -eiiicientgasification. rlhe fluidized bed or solid fuel `andfresulting charprovides an ideal reaction zone for the production of methane fromcarbon monoxide and vhydrogen, since the entire' reaction zone maybemaintained-at a uniform desired temperature.` As there is=no`appreciableconsumptionV of the Ac'oal particles in the vfiuidized fbedand no ash production, there kfisno problem of carbon loss asltheconventional iiuid' bed gasifier.-v Heat transfer surfaceslmay. beprovided in them'ethanization zone forl accurate control of thetemperature therein. Heat from' -the'fmethahization zone may be used tovaporize the slurry: feed stream;A

Since the: bed of solid particles of carbonaceous material inthemethanization zoneismaintained in/ a`Y highly' turbulent condition.fresh coal is rapidly dispersed in a large volume-of carbonized coal orchar. Under these conditions, araw caking, 'coal passes through theplastic vstage with a minimum of agglomeration.` Heattransfersurfacesa're kept Vclean 'by the abrasivel action "of thefiuidized particles.

The process of this invention' `produces a" fuel gas of Vequal or higherheating-valuethanfcomparable processes in which gasification Withsteamand oxygen is carried out in a dens'epliase, el g.; in a i-luidiized ormoving bed,"with' an appreciable Methane produced by this reaction andsaving in oxygen and steam. The permissible oXygen-to-steam ratio in thegenerator is considerably higher than for the conventional dense phasegasification reactors while, at the same time, the oxygen-to-fuel ratiois lower. Since oxygen and, to a lesser extent, steam requirements aresignificant factors in the cost of synthetic fuel production, thepresent process materially improves the economy of the production offuel gas of high heating value.

The overall steam requirements for the process range from about 0.8 toabout 2.0 pounds per pound of solid fresh fuel while the free oxygenrequirements range from about 0.1 to about 0.8 pounds per pound of solidfresh fuel. Pressures may vary from about 150 to about 750 pounds persquare inch gauge, or higher.

In a preferred embodiment of this invention, coal in particle form ismixed with suficient water to form a iiuid suspension or slurry. Theslurry is passed through a tubular heating zone wherein it is heated toa temperature at least sufficient to vaporize the water. Combined watercontained in the coal need not be completely removed in the heatingstep. The heating step produces a dispersion of powdered coal in steamand at the same time may distill some of the volatilizable constituentsfrom the coal.

The quantity of liquid admixed with the coal to form the suspension mayvary considerably depending upon process requirements and the feedmaterial. A minimum of about percent water by Weight is required to forma fluid suspension of coal. The liquid content of the suspension may becontrolled by first mixing the solid with a quantity of liquid in excessof the required quantity and adjusting the consistency to the desiredvalue by removal of excess liquid in a conventional thickener. Thesuspension is readily pumped with suitable equipment, e. g., with adiaphragm type pump, of the type commonly used for handling similarsuspensions of solids. The suspension may be made up at a point somedistance away from the processing site and pumped to the site in apipeline.

A catalyst for the methanization reaction, for example, iron oxide, maybe added to the slurry. Also fluxing agents, e. g., lime, silica,alumina, etc., may be added to decrease the fusion temperature of theash.

Some coals require substantial theoretical amounts of steam for theproduction of hydrogen and carbon monoxide by reaction with steam andoxygen at temperatures within commercially attainable limits 2000 F. to3000 FJ. Others contain Water in suiiicient quantity or even in excessof the theoretical requirements. Anthracite is an example of the former,requiring a considerable quantity of steam, for example, 30 percent byWeight. Lignite is an example of the latter, often containing more thanthe theoretical requirement of water. Water in excess of the theoreticalrequirement is not detrimental to the gasification reaction. Whileanthracite, because of its relatively high steam requirement, is anexcellent feed material for the process of this invention, lignite mayalso be used.

Anthracite silt may advantageously be used as a feed material for thepresent process. Anthracite silt is a term applied to the fine particlesof coal and associated impurities, obtained as a by-product in themining, handling, and sizing of anthracite coal. Anthracite silt may beused in the present process Without preliminary grinding.v It ranges insize from about 13e inch aver- 4 age diameter, to about 200 mesh, thebulk of the material falling Within the range of t inch to mesh.

The size of the coal particles fed to the heating step is not ofespecial importance to the successful operations of the invention.Particles of a size which may be passed through the heater tubes Withoutdifculty may be used, i. e., particles having an effective diameter lessthan onethird the pipe diameter. Generally, it is preferable to useparticles less than about one-quarter inch in average diameter. Sincethe heating of the dispersion under turbulent flow conditions results indisintegration of the coal, costly pulverization by mechanical means iseliminated. It is contemplated in most applications of this process thatthe coal will be reduced only to a particle size such that it may bereadily handled as a suspension or slurry. The coal may be crushedmechanically to about one-fourth inch in average diameter with" arelatively small expenditure of power. Further mechanical reduction insize becomes progressively more expensive, pulverization requiring largeexpenditures of power. It is evident that this process possessesimportant advantages over conventional methods which involve separatepulverization and carbonization.

The linear' velocity of a liquid suspension at the inlet to the heatingcoil should be within the range of from about l/2 foot to about l0 feetper second, suitably about l to 2 feet per second. The velocity ofgaseous dispersions as at the outlet of the coil depends upon thepressure and temperature of the dispersion.

The temperature at the outlet of the heating coil may range from about250 to 1500 F. or higher. The temperature preferably is at leastsuflicient to insure vsubstantially complete vaporization of liquidpresent in the dispersion by the time it is discharged fromthe heatingzone. Preferably a temperature within the range of 600 to 1400 F. isattained at the outlet of the coil. The higher temperatures, withinpractical limits, are usually advantageous. The extent of carbonization,i. e., distillation of volatilizable constituents from the coa-l, may becontrolled by control of the temperature.

Pressure, in itself, is not critical in the heating step. Thetemperature and pressure relationships affecting vaporization are wellknown. 1t is desirable to operate the heating zone at a pressuresomewhat higher than the operating pressure of the gasication zone. Inthe generation of fuel or synthesis gas, it is often desirable tooperate the gasification step at an elevated pressure, for example, 300to 600 pounds per square inch. The heating and pulverizing step may beoperated at a corresponding pressure sufficient to insure flow throughthe heating coil and into the generator at the desired rate. Aconsiderable pressure drop takes place in the heating zone due toresistance to flow. This drop may be on the order of, for example, 100pounds per square inch. Often it is desirable to reduce the pressuresuddenly in the heating zone or at its outlet to enhance thevaporization and disintegration actions of the heating step.

Part of the vapors may be separated from the powdered solid before it isfed into the generator or part of the solid may be separated from thegasiform dispersion. Separation of powdered solids from gases or vaporsmay be effected in a number of Ways. `A cyclone separator is generallyeffective for removal of solids from gases.

5 Very fine particles may be 'separated with a Cottrell precipitator.Less desirable are sepa.- rators of the filter or liquid contact type.

A number of advantages are obtained by this method of operation.Pulverization and preheating of the coal, and generationand preheatingof the steam for the gasiiication reaction may be accomplished in asingle heating step. Additionally, the coal may be subjected todistillation conditions. When dispersed in a liquid `to form a slurry,the carbonaceous solid maybe readily transported and subjected vtoelevated pressure. Since the slurry mayv be handled as a liquid,troublesome lock hoppers and similar devices are eliminated and replacedsimply by a slurry mixe-r and a pumpr Another advantage results from thefact that, in a dispersion, the quantity .of coal fed to the process maybe accurately metered.

The. invention will .be more readily understood' from. the followingdetailed description and the. accompanying drawing. In Vthe detaileddescrip` tion of illustrative operations involving the presentinvention, coal is taken as a preferred fuel and Water as a preferredliquid for forming the dispersion.

The ligure is a diagrammatic elevational view illustrating a preferredmethod of carrying out the process of the present invention.

With. reference to the gure, coal in particle form is introduced throughline I into storage hopper 2 from which it may be passed through line 3into mixer 4. Sufficient water to form a uid slurry of coal in water isadmitted to the mixer through line E. The slurry is withdrawn from themixer 4 .to a pump i and forced under pressure through a heating coil 8wherein it is heated to a temperature at least suiiicient to vaporizethe Water. The resulting dispersion of powdered coal in steam isintroduced into conduit 9 and thence into vessel i Vessel I is apressure vessel wherein hot gases comprising carbon oxides and hydrogenresulting from the gasification of solid fuels with oxygen and steam arecontacted with fresh coal and its char in a dense phase fluidized bed. Acooling coil II is provided in vessel I0 to remove excess heat therefromand to control the temperature at which the methanizationzone isoperated. IIn the vessel I0, carbon monoxide and hydrogen interact inthe presence of the solid fuel to produce methane. At the same time,volatilizable materials are distilled from the coal and admixed with thegases resulting from the gasification with steam and oxygen and themethanization reaction.

The resulting mixture of gases passes through line I2 to a cycloneseparator I3. In the separator I3, solid particles of coal which may becarried over from the uidized bed in vessel I0 are separated from thegases. The fine particles so recovered are passed through line I4 tomixer 4 into admixture with particles of fresh coal from line 3. Thegases from separator I3 pass through line I5 into heat exchange with theslurry in the heating coil 8 to provide at least a portion of the heatrequired for heating the slurry. The gases are then discharged from thesystem through line I6 as raw fuel which, after suitable purificationsteps for the removal of water, condensible oils and tars, is suitablefor industrial and household heating.

Char from the vessel I0 is withdrawn through line I'I and introducedinto the gasification zone I8 into admixture with oxygen and steamentering through line I9. The gasification zone is operated as a :lio-wgenerator with the reactants in dilute phase. The resulting gases fromthe gasification zone pass through line 9 into vessel Ill. Slag isdischarged from the gasification zone I9 through line 2B.

Example Buckwheat coal having the following analysis is used in theprocess of this invention:

Percent Percent Percent Llggfe Dry and Proximate Analysis as Dried Y andAs'h Mineral Received at .10590. Free Matter Free Moisture 3. 3'Volatile Matter.. 4. 7 4. 9 5. Fixed Carbon. 78.1 80. 7 94.

13. 9 14.4 Ultimate Analyst Ash 13.9 14.4 y Sulfur 0. 6 0.6 t). 7Hydrogen 2. 5 2. 3 2. B Carbon--. 76. 7 79. 3 92. 7 Nitrogen.. 0. 8 .80. 9 Oxygen 5. 5 2. 6 3. 1 Calorie Value, B. t. u.

per lb l2, 730 l2, 730 14, 870 15,040

A slurry is made up using one pound of water per pound of coal. Theslurry is charged through a heating coil wherein it is heated to about1100 F. and charged into a iiuidized bed of char in a methanization zonemaintained at about 1160 F. and 600 pounds per square inch gauge. Theslurry is passed in indirect heat exchange with the iiuidized bed ofchar in the methanization zone.

The gasification zone is operated at about 2320 F. and 600 pounds persquare inch gauge. Steam and oxygen are preheated to about 620 F. andadmixed with char drawn directly from the methanization zone. Thequantities of steam and oxygen fed to the gasier correspond to 0.773pound steam and 0.760 pound of an oxygen concentrate containing 99.2percent oxygen and 0.8 percent nitrogen, by volume, per pound of rawcoal, as received, fed to the system. The slag is withdrawn from thegasier as a liquid in an amount corresponding to 0.150 pound per poundof feed.

The char from the methanization zone amounts to about 0.907 pound perpound of raw coal. About 0.021 pound of recovered fines is separatedfrom the product gas and admixed with the fresh feed.

The gas from the gasication Zone at 2320 F. has the followingapproximate composition:

Volume percent lydrogen 26 Carbon monoxide 49 Water vapor 15 Carbondioxide 10 All of this gas passes to the methanization zone. The totalproduct gas from the methanization zone has the following approximatecomposition:

- Volume percent Hydrogen 1l Methane 12 Water vapor 44 Carbon monoxide 3Carbon dioxide 30 equivalent to about 14.2 standard cubic feet per poundof raw coal of the following composition:

Volume percent Hydrogen 40 Methane 46 Carbon monoxide 12 Nitrogen 1 1Water vapor and carbon dioxide 1 The fuel gas has a gross heating valueof about 611 B. t. u. and a net heating value of 548 B. t. u. perstandard cubic foot.

`Gloviously many modifications and variations of ;the invention ashereinabove setJ forth may be made without departing from the spirit andscope thereof and, therefore, only such limitations should be imposed asare indicated in the appendedclaims.

I claim:

1. In a process for the generation of fuel gas from a solid carbonaceousfuel containing volatilizable constituents, the improvement whichcomprises admixing said solid carbonaceous fuel in particle form withsuiicient water to forma fiuid suspension, passing said suspensionthrough a heating zone at an elevated temperature such thatsubstantially all of the water is vaporized thereby -forrning adispersion of coal in steam, passing the resulting dispersion into afluidized bed of solid carbonaceous material in a methanization zoneinto contact with carbon monoxide and hydrogen at a temperature withinthe range of from about 900 1o about 1800" F. whereby carbon monoxideand hydrogen are converted to methane and Volatilable constituents ofsaid solid carbonaceous material are distilled therefrom, withdrawingcarbonaceous material from said methanization zone and passing it intocontact with oxygen and steam in dilute phase in a gasification zonemaintained at a temperature within the range of from about 2000 to about3000 F., passing the resulting gases comprising carbon monoxide andhydrogen from the'gasiiication zone into the methanization zone as thesource of carbon monoxide and hydrogen therefor, and discharging thegaseous products of the methanization zone as the raw product fuel gas.

2. A process as defined in claim 1 wherein at least a portion of theheat requirements of said heating zone is obtained from saidmethanization zone by indirect heat exchange.

3. A process as defined in claim 1 wherein said methanization zone ismaintained at a temperature within the range of from about 1000 to about1500 F.

4. A process as defined in claim 1 wherein the gasification zone andmethanization zone are operated at a pressure within the range of fromabout to about 750 pounds per squareinch gauge.

5. In a process for the generation of fuel gas from a solid carbonaceousfuel containing volatilizable constituents, the improvement whichcomprises admixing said solid carbonaceous fuel in particle form withsuicient Water to form a iiuid suspension, passing said suspens ionthrough a heating zone at an elevated temperature such thatsubstantially all of the Water is vaporized thereby forming a dispersionof coal in steam, separating at least a portion of the steam from thesolid carbonaceous particles, passing the solid carbonaceous Particlesinto a fluidized bed of solid carbonaceous material in a methanizationzone into contact with carbon monoxide and hydrogen at a temperaturewithin the range of from about 900 to about 1800 F. whereby carbonmonoxide and hydrogen are converted to methane and volatilizableconstituents of said solid carbonaceous material are distilledtherefrom, withdrawing carbonaceous material -from said methanizationzone and passing it into contact with oxygen and steam in dilute phasein a gasification zone maintained at a temperature within the range offrom about 2000 to about 3000 F., passing the stream separated from thesolid carbonaceous particles to the gasification zone to supply at leasta portion of the steam thereto, passing the resulting gases comprisingcarbon monoxide and hydrogen from the gasification zone into themethanization zone as the source of carbon monoxide and hydrogentherefor, and discharging the gaseous products of the methanization zoneas the raw product fuel gas.

DU BOIS EASTMAN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,414,586 Egloil Jan. 21, 1947FOREIGN PATENTS Number Country Date 286,404 Great Britain Mar. 8, 1928503,158 Great Britain Apr. 3, 1939 578,711 Great Britain vJuly 9, 1946

1. IN A PROCESS FOR THE GENERAION OF FUEL GAS FROM A SOLID CARBONACEOUSFUEL CONTAINING VOLATILIZABLE CONSTITUENTS, THE IMPROVEMENT WHICHCOMPRISES ADMIXING SAID SOLID CARBONACEOUS FUEL IN PARTICLE FORM WITHSUFFICIENT WATER TO FORM A FLUID SUSPENSION, PASSING SAID SUSPENSIONTHROUGH A HEATING ZONE AT AN ELEVATED TEMPERATURE SUCH THATSUBSTANTIALLY ALL OF THE WATER IS VAPORIZED THEREBY FORMING A DISPERSIONOF COAL IN STEAM, PASSING THE RESULTING DISPERSION INTO A FLUIDIZED BEDOF SOLID CARBONACEOUS MATERIAL IN A METHANIZATION ZONE INTO CONTACT WITHCARBON MONOXIDE AND HYDROGEN AT A TEMPERATURE WITHIN THE RANGE OF FROMABOUT 900 TO ABOUT 1800* F. WHEREBY CARBON MONOXIDE AND HYDROGEN ARECONVERTED TO METHANE AND VOLATILABLE CONSTITUENTS OF SAID SOLIDCARBONACEOUS MATERIAL ARE DISTILLED THERE-